I just bought my Christmas poinsettias for this year (2012) and got a great deal at Home Depot. A nice, full, six inch pot for less than $5.00 ( this was in 2012, they are much pricier now) and a very full planter of poinsettias plus variegated ivy for less than $15.00. Home Depot also had Christmas cactus, which I thought about getting... but decided I wanted to wait until later.
I couldn't resist the cut flower bouquet at Whole Foods Market, and brought home a very Christmas-y red, green, and white combination. It had pure white carnations that smelled lovely, dainty red roses, greenery, white stock, dark red chrysanthemums, some pink alstroemerias, and one flowering kale for good measure. I arranged them in a large, vintage, green glass vase.
I will probably buy another bouquet of flowers closer to Christmas day, for making a dining room centerpiece. I think that Whole Foods Markets, and Costco have the freshest flowers in the best available flowers for the money.
For greenery we shopped at Whole Foods Markets again (you can tell how much I love that store!). There was a bundle deal of tree, wreath, and garland - so we went for it. Not every WFM will have the same vendors and deals, but if you are in the Columbus, Ohio area, check it out (I don't know how long it lasts). I also like Sam's club for fresh wreaths, check to see if they have good ones this year.
In the Atlanta area of Georgia, Costco provides some fresh and economical greenery to decorate the house. They are now my go-to store for these items.
You get uneven quality at Lowes, but they did have some unique greenery, like kissing balls, and porch planters.
Hope you are enjoying the season as much as I am.